Difficulty: Easy
Correct Answer: 20, 30
Explanation:
Introduction / Context:
This is a classic two-part split constrained by a condition on reciprocals. The key is to convert the verbal condition into an algebraic equation in a single variable and solve a simple quadratic. Such questions appear frequently in number system sections of aptitude tests.
Given Data / Assumptions:
Concept / Approach:
Add the reciprocals using a common denominator and equate to 1/12. This yields a quadratic equation in x. Solve the quadratic to obtain two positive solutions, which are complementary parts summing to 50. Check both solutions for validity and verify the reciprocal condition numerically.
Step-by-Step Solution:
Start: 1/x + 1/(50 − x) = (50) / (x(50 − x)) = 1/12.Therefore, x(50 − x) = 600.Expand: 50x − x^2 = 600 → x^2 − 50x + 600 = 0.Solve: Discriminant D = 2500 − 2400 = 100; x = (50 ± 10)/2 → x = 20 or 30.
Verification / Alternative check:
Check 20 and 30: 1/20 + 1/30 = (3 + 2)/60 = 5/60 = 1/12. Condition satisfied exactly.
Why Other Options Are Wrong:
24, 26 give 1/24 + 1/26 ≠ 1/12; similarly 28, 22 and 36, 14 and 18, 32 do not satisfy the reciprocal sum constraint.
Common Pitfalls:
Algebra sign errors when forming the quadratic; forgetting both roots are valid and symmetric around 25; mixing reciprocal sum with arithmetic sum or difference.
Final Answer:
20, 30
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